Stall detection aims at detecting if a motor is not rotating or is blocked. Prior art methods for stall detection in a synchronous multiphase motor are based on back electromotive force (BEMF) measurements. When a synchronous multiphase motor is driven in sine mode, the sinusoidal BEMF voltage increases in a linear way with the speed of the motor. When the motor speed goes from normal to zero this can be detected by monitoring the BEMF drop. In prior art solutions the BEMF voltage is measured by using one floating phase on which the BEMF voltage can be measured. This has, however, as disadvantage that this floating phase is not contributing to the motor power. Besides decreasing the motor power, this also causes unwanted or noisy torque ripples.
Therefore, solutions are sought for stall detection whilst driving all phases of the multiphase motor. US20160013743A1, for example, discloses a method for stall detection based on motor current increase during stall. However, this does not work in all cases. This method cannot be used for low-speed motors with low-BEMF level. The current increase due to the absence of the low-BEMF is too small for reliable detection.
In view of these stall detection problems, there is room for improved methods and circuits for stall detection of a multiphase motor which is driven using sinusoidal micro-stepping.